1. Field of the Invention
This invention relates to new compounds of the diphenyl ether series possessing a very strong and selective herbicidal activity and to herbicidal compositions containing the new compounds as an active ingredient.
2. Description of the Prior Art
Many compounds of the diphenyl ether series have previously been examined to determine their effectiveness in practical use as herbicides. In many cases, the presence or absence, degree, mode of function, selectivity and duration of the herbicidal activities of these compounds differ with even a slight difference in chemical structure of the compounds such as type, number and position of substituents. Thus, it is extremely difficult to estimate or predict the herbicidal activity of these compounds from their similarities in chemical structure.
It is a well-known fact that some compounds of the diphenyl ether series are excellent herbicides. For example, 2,4-dichlorophenyl-4-nitrophenyl ether (referred to hereinafter as NIP) and 2,4,6-trichlorophenyl-4-nitrophenyl ether (referred to hereinafter as CNP) are widely used as herbicides in rice fields.
Ideal herbicides are required to exhibit on the one hand a very strong herbicidal activity to undesirable plants even at a low level of concentration and on the other hand an extremely low toxicity to useful plants. However, known herbicides developed hitherto still fail to meet fully either or both of these requirements. In recent years, the problem of environmental pollution has been raised in connection with the use of agricultural agents and the use of highly effective herbicides in small amounts has been recommended to minimize any possible environmental effect. Under these circumstances, there is a great demand for developing a new type of herbicide which fully meets the aforesaid requirements.